“Radon” sounds like a secret supervillain, and you could say that’s essentially what it is. An invisible, odorless gas, radon concentrates in homes and buildings, exposing those who breathe it in to the second-top cause of lung cancer in the U.S. The good news is radon testing is simple; high-radon homes can be mitigated or fixed – and free or reduced-cost testing is offered in many areas.

Invisible Carcinogen

“Radon is actually the leading environmental cause of cancer mortality in the United States,” says Bill Field, a professor of occupational and environmental health at the University of Iowa. “About 21,000 people die each year from it. People really underestimate its importance.”

Lung cancer is the only type of cancer with a proven association to protracted exposure to radon. “We have some suspicions it may be related to other types of cancers, but there are no studies that have conclusively shown that,” Field says.

As a cause of lung cancer in the U.S., radon is surpassed only by smoking. And people who smoke are even more vulnerable when exposed to radon. “If you’re a smoker and you live in a house with radon, your risk is geometrically higher than just being a smoker without it,” says Janice Nolen, assistant vice president for national policy at the American Lung Association. “The two together combine to worsen your risk of developing lung cancer.”

A Little Too Airtight

Today’s energy-efficient, airtight homes actually pull radon inside and trap it there, says Angel Price, associate director of Cancer Survivors Against Radon. “Your houses suck” is a phrase used in radon-training courses, she says, to illustrate how homes work as vacuums to draw radon in.

CanSAR was co-founded by Elizabeth Hoffman, who was diagnosed with radon-induced lung cancer in 2003 and died a decade later. Hoffman became an anti-radon advocate, testifying several times in front of Congress about the dangers of radon and the need for national awareness and action.

Each Home Is Different

The Environmental Protection Agency website includes a map of EPA radon zones, which color-codes counties into zones 1, 2 and 3. The areas in zone 1 have the highest predicted indoor radon screening levels. But the EPA notes that homes with elevated radon levels can be found in all three zones.

“The reality is, we do know that high levels can be anywhere,” Nolen says. “If you look at that map and go, ‘Hmm, I don’t live in one the highest-risk zones; I’m not going to worry about it,’ you’re missing the point. It can be a problem in any home in any neighborhood.”

Awareness of radon’s risk for lung cancer started by looking at miners who had been exposed to uranium, Nolen says. However, it wasn’t known that radon was also in homes until the mid-1980s, she says.

“The more we learned, the more we know that it is a risk in many, many homes,” Nolen says. “It can be in areas where you don’t think it’s a problem. Your neighbors may have tested and not had a problem. But you test because your situation may be very different, depending on your house.”

Field agrees: “I’ve looked at radon readings from every state,” he says. “There are homes that have very high radon concentrations, even though the state as a whole may not have a high concentration.”

Testing for Peace of Mind

Short-term testing evaluates home radon concentrations over roughly 24 hours, Nolen says. Her group recommends longer-term tests over several months. Radon levels can fluctuate, she says, so extended testing in your home gives a better representative sample.

“Then, if you have low levels, you can check every couple years,” Nolen says. “If you do some major renovations, you can check again. The most important thing is to do the test, to find out if you have high levels of radon.”

You can perform a simple DIY test on your home for about $15 a kit. “What’s really nice is, when you order a do-it-yourself test, it comes with very detailed instructions and graphics on how to perform the test,” Field says. “On how to place the test, the duration and how to return the test. A lot of tests include paid postage for sending the detector back to the laboratory for analysis.”

It only takes about three or four days to get results back, Field says, with an explanation of what they mean – whether radon concentrations are high or below the EPA’s action levels. Professional testing with more sophisticated methods is also available.

While January is the EPA’s National Radon Action Month, you can still tap into many free- or reduced-cost testing in locales including Nevada; Greenwich, Connecticut; and Macomb County, Michigan. Check your health department for radon-testing initiatives in your area.

Mitigation and Prevention

If your home’s radon levels are elevated, you can take steps the improve them. ​”Exposure is the concentration times the time you’ve been at the exposure,” FIeld says. “So you want to make every effort to decrease that exposure by eliminating the source.”

Mitigation is the process used to reduce radon concentration and prevent the gas from coming into your home, Field explains. Installing a mitigation system involves drilling a hole in your basement foundation or first-floor slab, and running a PVC pipe from a ground-level trench upward. An exhaust fan quickly draws radon from inside your home and sends it out through the roof.

“To me, radon is like a little dirty bomb that goes off in homes, but the dirty radioactive bomb is from Mother Nature,” Field says. “Radon outdoors is naturally occurring. Radon, when it’s coming into your home, is not.” Making new homes radon-resistant is a cost-effective way to be proactive, he says. “You’re talking about $500 extra when you build that home.”

Schools and Workplaces, Too

Radon isn’t just a hazard at home. Nearly 1 in 5 schools nationwide is estimated to have at least one schoolroom with a short-term radon level above​ the EPA’s action level, according to the agency’s website. Office buildings, college dorms, daycare facilities – anywhere people routinely spend a large portion of their day is a potential source of radon exposure.

“It happens most frequently at home because we spend most of our time indoors at home, especially children,” Nolen says. “And the longer you’re exposed, that means the more you’re breathing in this carcinogen.”

Dorms or office buildings should also be tested, Field says, especially if they’re underground or on the first level. “Any building where people are going to spend any substantial period of time should be tested to make sure they’re safe,” he says. “Many universities will respond if people request a test. If people have concerns about radon, the university health office will come out and do testing of that building or that dorm to make sure that levels are low.”

Every structure should be tested, Price says. “There are different protocols for testing multifamily homes,” she notes. “And there’s a school testing protocol. There are different ways to test and different methodologies.”

Similarly, you can talk to your employer about workplace testing if you are concerned. Or you can call the Nation Radon Hotline at 800-557-2366 (or 800-55R-ADON) with any questions.​

Reducing Radon

The American Lung Association is leading a national workgroup on radon policy, which released its National Radon Action Plan in November 2015. “Incorporating radon testing, radon mitigation and radon-resistant construction into systems that govern purchasing, financing, constructing and renovating homes and other buildings” are among the plan’s goals.

On an individual level, Nolen says, “Radon is [a hazard] to put at the top of your list of things to deal with, especially if you’re concerned about your family’s health.”

Price concurs: “It’s a whole lot cheaper to mitigate your home and to test than have lung cancer,” she says. “A lot less expensive and a lot less painful.”